This invention relates to improvements in balls for sport, such as balls used in volleyball, basketball, etc.
The ball is filled with air by inserting an air injection needle into a hole for air injection needle of an air injection valve attached to the rubber inner tube of the ball and by penetrating the leading end of the needle into a slit of the air injection valve, which is usually closed to prevent air from escaping from the interior of the ball.
In the construction of the conventional ball, the air injection valve is attached to the rubber inner tube of the ball so that its upper end portion projects from the rubber inner tube. An envelope or outer layers comprising a yarn-winding layer, a rubber cushion layer and a skin layer made of leather or rubber are provided on the inner tube at the overall circumferential surface thereof, except for the projecting upper end portion of the valve. The outer layers surround the valve at the upper end portion thereof and the outer surface of the outermost skin layer is so adapted as to be flush with or lie on the same plane as the upper end surface of the valve. Thus, the skin layer and the upper end portion of the valve form a continuous smooth surface.
Although the upper end portion of the valve and the skin layer form a smooth surface, since the upper end surface of the valve is exposed and made of a material harder than that of the skin layer, the exposed upper end surface feels hard. Therefore, when the exposed upper end portion strikes the body of a player especially the hands and legs during play, the player feels pain. Especially in the case of volleyball, when a player receives a strongly served ball or blocks a spiked ball, the player suffers acute pain in that part of the body which has been struck by the exposed upper end portion of the valve. This often would result in a bruise.